JDK5.0允许象C语言那样直接用printf()方法来格式化输出,并且提供了许多参数来格式化输入,调用也很简单:
<table width="588" border=1 cellPadding=0 cellSpacing=0 bgColor=#e6e6e6 style="BORDER-RIGHT: medium none; BORDER-TOP: medium none; BACKGROUND: #e6e6e6; BORDER-LEFT: medium none; BORDER-BOTTOM: medium none; BORDER-COLLAPSE: collapse; mso-border-alt: solid windowtext .5pt; mso-padding-alt: 0cm 5.4pt 0cm 5.4pt"> <tr> <td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 0.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 0.5pt solid; WIDTH: 426.1pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; BACKGROUND-COLOR: transparent" vAlign=top width=584>System.out.format("Pi is approximately %f", Math.Pi);
System.out.printf("Pi is approximately %f", Math.Pi);
printf()和
format()
方法具有相同的功能. System.out
是 java.io.PrintStream的实例
. PrintStream
, java.io.PrintWriter
, 和 java.lang.String
每个类都有四个新的格式化方法:
format( String format, Object... args);
printf( String format, Object... args);
format( Locale locale, String format, Object... args);
printf( Locale locale, String format, Object... args);
同时,以前的formatter类也提供了更完善的方法来格式化,例如:
formatter.format("Pi is approximately %1$f," + "and e is about %2$f", Math.PI, Math.E);
格式化元素的构成如下:
<table style="BORDER-RIGHT: medium none; BORDER-TOP: medium none; BACKGROUND: #e6e6e6; BORDER-LEFT: medium none; BORDER-BOTTOM: medium none; BORDER-COLLAPSE: collapse; mso-border-alt: solid windowtext .5pt; mso-padding-alt: 0cm 5.4pt 0cm 5.4pt" cellSpacing=0 cellPadding=0 bgColor=#e6e6e6 border=1> <tr> <td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 0.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 0.5pt solid; WIDTH: 426.1pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; BACKGROUND-COLOR: transparent" vAlign=top width=568>%[argument_index$][flags][width][.precision]conversion
其中:
argument_index是一个正整数,说明了参数的位置,1为取第一个参数
width表示输出的最小字母个数
precision代表数字的小数位数
conversion代表被格式化的参数的类型:
f
float,
t
time
d
decimal
o
octal
x
hexadecimal
s
general
c
a Unicode character
以下是个例子:
<table style="BORDER-RIGHT: medium none; BORDER-TOP: medium none; BACKGROUND: #e6e6e6; BORDER-LEFT: medium none; BORDER-BOTTOM: medium none; BORDER-COLLAPSE: collapse; mso-border-alt: solid windowtext .5pt; mso-padding-alt: 0cm 5.4pt 0cm 5.4pt" cellSpacing=0 cellPadding=0 bgColor=#e6e6e6 border=1> <tr> <td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 0.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 0.5pt solid; WIDTH: 426.1pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; BACKGROUND-COLOR: transparent" vAlign=top width=568>package format;
import java.util.Formatter;
public class UsingFormatter {
public static void main(String[] args) {
if (args.length != 1) {
System.err.println("usage: " +
"java format/UsingFormatter ");
System.exit(0);
}
String format = args[0];
StringBuilder stringBuilder = new StringBuilder();
Formatter formatter = new Formatter(stringBuilder);
formatter.format("Pi is approximately " + format +
", and e is about " + format, Math.PI, Math.E);
System.out.println(stringBuilder);
}
}
//控制台调用
java format/UsingFormatter %f
//输出
Pi is approximately 3.141593, and e is about 2.718282
//控制台调用
java format/UsingFormatter %.2f
//输出
Pi is approximately 3.14, and e is about 2.72
//控制台调用
java format/UsingFormatter %6.2f
//输出(有空格来填补长度)
Pi is approximately 3.14, and e is about 2.72
//控制台调用
java format/UsingFormatter %1$.2f
//
输出
Pi is approximately 3.14, and e is about 3.14
//改变区域设置
package format;
import java.util.Formatter;
import java.util.Locale;
public class UsingFormatter {
public static void main(String[] args) {
if (args.length != 1) {
System.err.println("usage: " +
"java format/UsingFormatter <format string>");
System.exit(0);
}
String format = args[0];
StringBuilder stringBuilder = new StringBuilder();
Formatter formatter = new Formatter(stringBuilder,
Locale.FRANCE);
formatter.format("Pi is approximately " + format +
", and e is about " + format, Math.PI, Math.E);
System.out.println(stringBuilder);
}
}
//控制台调用
java format/UsingFormatter %.2f
//输出
Pi is approximately 3,14, and e is about 2,72
//采用format,printf的可替代写法
package format;
public class UsingSystemOut {
public static void main(String[] args) {
if (args.length != 1) {
System.err.println("usage: " +
"java format/UsingSystemOut <format string>");
System.exit(0);
}
String format = args[0];
System.out.format("Pi is approximately " + format +
", and e is approximately " + format, Math.PI, Math.E);
}
}
//控制台调用
java format/UsingSystemOut %.2f%n
//输出
Pi is approximately 3.14
, and e is about 2.72
对时间的格式化用字母t来代表,通常在t后面加上特殊的字符来显示时间的某个部分:
<table style="BORDER-RIGHT: medium none; BORDER-TOP: medium none; BACKGROUND: #e6e6e6; BORDER-LEFT: medium none; BORDER-BOTTOM: medium none; BORDER-COLLAPSE: collapse; mso-border-alt: solid windowtext .5pt; mso-padding-alt: 0cm 5.4pt 0cm 5.4pt" cellSpacing=0 cellPadding=0 bgColor=#e6e6e6 border=1> <tr> <td style="BORDER-RIGHT: windowtext 0.5pt solid; PADDING-RIGHT: 5.4pt; BORDER-TOP: windowtext 0.5pt solid; PADDING-LEFT: 5.4pt; PADDING-BOTTOM: 0cm; BORDER-LEFT: windowtext 0.5pt solid; WIDTH: 426.1pt; PADDING-TOP: 0cm; BORDER-BOTTOM: windowtext 0.5pt solid; BACKGROUND-COLOR: transparent" vAlign=top width=568>tr hour and minute,
tA
the day of the week
tB
the name of the month
te
the number of the day of the month
tY
the year
//eg.
package format;
import java.util.Calendar;
public class FormattingDates {
public static void main(String[] args) {
System.out.printf("Right now it is %tr on " +
"%
Calendar.getInstance());
}
}
//说明:“<”指示采用的参数为前一个被格式化的参数
//输出
Right now it is 01:55:19 PM on Wednesday, September 22, 2004.
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